1. Field of the Invention
The present invention relates to a transmission line coding method and a transmission line decoding method for line coding/decoding sound signals used by electronic equipments, and an apparatus which uses these methods.
2. Description of the Related Art
There have been known a transmission line coding method and a transmission line decoding method for line coding/decoding sound signals defined in RCR-STD28 (PHS standards) of the Association of Radio Industries and Businesses (ARIB). FIG. 8 is a block diagram showing the key configuration of a communications system which performs this type of line coding/decoding.
The sending party has an ADPCM encoder 701 and a CRC code adder 702. The sending party adds CRC check code bits to all of sound signals subjected to compression coding by way of the ADPCM mode per transmission frame and then transmits. The receiving party has a CRC code checker 703 for detecting a transmission error, an ADPCM decoder 704 for decoding a received transmission frame, and a muting circuit 705 for muting sounds to be decoded in the event of a transmission error.
However, in the conventional communications system mentioned above, sounds are muted for the duration of a frame where a transmission error has taken place. This results in interruption of sounds in the meantime thus degrading the speech quality. Moreover, transmission frame has to be initialized mutually by using ARQ (Automatic Repeat reQuest) with bidirectional communications between the sending party and the receiving party. This results in a complicated system configuration.